Power Module Leadframe with Stress Buffering Layer
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Solution Overview
Problem
Conventional power modules face limitations in miniaturization and large current capacity due to the constraints of electric wiring, with existing thickening methods and materials like aluminum wires and copper wires failing to adequately address the need for increased current density and reduced volume, particularly in electric vehicles and hybrid vehicles.
Innovation Solution
The implementation of a power module with a leadframe structure that includes a stress buffering layer with a low coefficient of thermal expansion (CTE) to buffer the CTE difference between the semiconductor device and the leadframe, using materials like Fe—Ni based alloys and Ni—Mo—Fe based alloys, and employing laser welding or spot welding techniques to connect the leadframe to the stress buffering layer, which can have an L-shape or U-shape cross-sectional structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum wires with larger diameter (500 μm) are used to thicken the wire, then the current capacity is improved, but the mounting volume increases and miniaturization is hindered
Solution Approach 1:
The patent changes the material parameter from aluminum to copper, which has higher electrical conductivity and current density. This allows achieving the same current capacity with a smaller wire diameter, thus reducing mounting volume while maintaining reliability
Solution Approach 2:
The patent employs a composite structure consisting of a copper wire embedded in a resin layer, which is then bonded to the leadframe. This composite approach allows the copper wire to provide high current density while the resin provides mechanical support and insulation, enabling miniaturization without sacrificing current capacity
2Reliability
If copper wires are used to reduce resistance and improve electrical conduction, then the electrical conduction is improved, but the cost increases
Solution Approach 1:
The patent applies copper wiring selectively only in the high-current paths where it is most needed for reducing resistance, while other parts of the module can use simpler aluminum wiring or leadframe traces. This localized application of copper minimizes the amount of expensive material used while still achieving the electrical conduction benefits
Solution Approach 2:
The patent uses a copper wire that is embedded in resin and then bonded to the leadframe, creating a replicated structure that maintains the electrical conduction properties of copper while allowing for standardized manufacturing processes. This approach enables cost-effective production through repeatable assembly steps
3Reliability
If aluminum ribbons with larger width (12 mm) and thickness (0.5 mm) are used, then the electrical conduction is improved, but the mounting volume increases
Solution Approach 1:
The patent changes the dimensional parameters of the conductor from large-width aluminum ribbons to smaller-diameter copper wires. Copper's superior conductivity allows achieving the same electrical conduction performance with significantly reduced cross-sectional area, thus reducing mounting volume while maintaining reliability
4Manufacturing precision
If laser welding is used to connect leadframe to stress buffering layer, then the manufacturing precision is improved, but the risk of damaging semiconductor device increases
Solution Approach 1:
The patent introduces a stress buffering layer as an intermediary component between the leadframe and the semiconductor device. This layer serves multiple functions: it provides a compliant bonding surface that reduces welding stresses, protects the semiconductor device from direct laser exposure and thermal damage, and buffers mechanical stresses from thermal expansion differences. This intermediary structure enables the use of precise laser welding while protecting the sensitive semiconductor device
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables miniaturization, increased current capacity, reduced costs, and improved yield by minimizing welding variations and preventing damage to semiconductor devices, while allowing for high-temperature operation without the need for bonding wires.
Implementation Method 1
a stress buffering layer disposed on an upper surface of the semiconductor device, and capable of buffering a coefficient of thermal expansion (CTE) difference between the semiconductor device and the leadframe
Implementation Method 2
employing laser welding or spot welding techniques to connect the leadframe to the stress buffering layer
Implementation Method 3
SiC power modules can conduct a large electric current
Data Source
AI summary
The power module includes: a first metallic circuit pattern, a semiconductor device disposed on the first metallic circuit pattern; a leadframe electrically connected to the semiconductor device; and a stress buffering layer disposed on an upper surface of the semiconductor device, and capable of buffering a CTE difference between the semiconductor device and the leadframe. The leadframe is connected to the semiconductor device via the stress buffering layer, a CTE of the stress buffering layer is equal to or less than a CTE of the leadframe, and a cross-sectional shape of the stress buffering layer is L-shape. There is provided: the power module capable of realizing miniaturization and large current capacity, and reducing cost thereof by using leadframe structure, and capable of reducing a variation in welding and improving a yield without damaging a semiconductor device; and a fabrication method for such a power module.